Injectable biomaterials materials

J. Temenoff, A. Mikos, Injectable biodegradable materials for orthopedic tissue engineering. Biomaterials 21 (2000) 2405-2412. 

In this category of injectable biomaterials, the gel is formed between the liquid monomers or macromers and a suitable polymerization/crosslinker initiator in response to either ionic or pH changes. Advantages of these kinds of materials include easy placement and subsequent polymerization to fill complex shaped defects that otherwise would be difficult to fill, improved adhesion of the polymer to the surrounding tissue due to close mechanical interlocking with the micro-roughened surface of the tissue. 

Abstract This chapter focuses on the vascular applications of injectable biomatetials. Two clinically relevant vascular conditions, cerebral arteriovenous malformations and intracranial aneurysm, will be discussed in terms of endovascular embolization. This chapter then outlines available embolic materials used to treat each condition, as well as highlighting new injectable biomaterials developed for embolization purposes. 

Shape memory polymers make up another class of injectable biomaterials for vascular applications, yet are relatively new in the field of endovascular embolization. Shape memory polymers are chemically structured so that they are able to reversibly take on a different physical shape in response to some stimuli (Small et al, 2007). Usually these different shapes include a compact form and an expanded form of the polymer. In the case of endovascular embolization, the expanded polymer can be pre-formed to fit specific contours of an individual aneurysm (Ortega et al, 2007). Upon interacting with some type of stimuli, such as heat or cold, the material is compacted into a shape that can be delivered through a microcatheter. The process of using shape memory polymers to embolize an aneurysm is shown in Fig. 7.5, along with samples of expanded SMPs (Ortega et al, 2007). 

The two most important areas of research when developing an injectable biomaterial for potential human use are (1) material characterization and (2) biocompatibility testing. Material characterization requires extensive rheological testing to assess a material s delivery performance and mechanical stability. The following lists summarize the general material characterization tests required by the FDA. 

In vitro modeling and ultimately in vivo testing are the final hurdles in the optimization of an injectable biomaterial. Model testing provides a complete picture of the injectability, control, and implant material characteristics. Can the... 

The IDE submission is the cmcial hurdle and major milestone that transitions a promising material into a viable and testworthy medical device. The IDE s format is a testament to this transformation. The first half of the submission is a detailed report of the injectable biomaterial s evolution and optimization -including all background data and all reports of prior investigation. This section includes the history of the material, all current mechanical and chemical testing, in vitro and in vivo modeling, and biocompatibility results. The second half of the submission, however, focuses on the injectable biomaterial as a device. This... 

Table 15.1 Schematic illustrating the four classes of injectable biomaterials reviewed in this chapter. Materials are divided into those that gel /Vis/tt/due to physical forces and those that cure by formation of chemical bonds...

Self-assembling injectable biomaterials also undergo gelation or phase-separation without chemical crosslinking reagents as described previously for environmentally responsive materials. Phase-separation of either hydrophobic bulk material or hydrophobic domains of amphiphilic molecules is a frequently applied mechanism by which self-assembly proceeds. 

Considerable interest exists in developing implantable and injectable biomaterials for drug delivery, tissue reconstruction and engineering [1]. In particular, biopolymer-based materials are the most attractive choice for such medical applications. This is primarily because they are easily pro-cessable, which could allow less or non-invasive therapeutic procedures. Most biomaterials produced as carriers for drug delivery or scaffolds for tissue reconstruction are intended... 

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